Ultimately, the value of papers relative to the watch depends on which model you are dealing with. The higher the collectibility/value/demand for the item, the more important it becomes to have a full, complete package (i.e. box, papers, hang tags, calendar, etc. PLUS RSC papers for service history). And it also depends on the brand as well; with Rolex, having this provenance is critical from a collector's/investor's standpoint. I've seen some examples differ 30%+ in price with or without these items. For brands such as Patek, it's a little less important to have the original papers as they can issue an extract from the archives if you send in the watch.
The thing with RSC papers alone is that it's not exactly what collectors consider to be a reflection on provenance. Granted, it proves that a watch has been in and out of a Service Center and has received a clean bill of health; however, it does not guarantee that a watch has been tampered with after the service has been done. Case in point- RSC's have stopped documenting exotic dialed watches as it has become common place for unscrupulous individuals to obtain paperwork confirming the presence of a certain dial type (i.e. red sub, DRSD, Newman, etc) and to then swap dials with a repaint or aftermarket dial and sell as original; the ramifications coming back to the RSC as a liability is something that Rolex wanted to wash it's hands of; as they had provided statement in writing of a certain dial which sells at a premium to be authentic it holds them accountable. Also, it has been known that some of the service centers were servicing watches with non-original dials as well, and simply letting them pass through. So, in this sense, the RSC paperwork is not what one considers definitive and why some collectors tend to pass on pieces that come only with RSC papers.